Automatic cameras now widely known in the art provide for automatic focusing and/or automatic lens aperture setting attendant to operation of the shutter release system. Such systems typically provide, upon initial operation of the shutter release button, a distance sensing and an illumination sensing operation. The former sensing operation produces an electrical control signal condition in the camera circuitry indicative of the distance to the object, and the latter sensing operation provides a similar control signal condition indicative of the brightness of the object under ambient illumination.
Responsively to these two sensing operations, the lens system is mechanically driven through a range of positions. Frequently a multi-position electrical contactor or synchronously driven potentiometer is used to provide an electrical signal condition indicative of the instantaneous lens position. The range control signal and the position-indicating signal condition are compared, by associated control circuitry to terminate the lens focus drive at the appropriate point. An aperture or shutter control system is similarly set into a state of motion to be similarly terminated at a position which will govern the degree of exposure of the film. This latter feature may take a variety of forms, such as a rotating drive for a conventional iris-type aperture. In the alternative it may also control exposure by controlling the action of the shutter itself. This shutter control may take a variety of forms, including controlling the separation between the two curtains of a focal-plane shutter, controlling the stroke length of an impulsively actuated shutter blade so as to govern the time necessary for it to return to a closed position, or the duration of the engagement time of a shutter blade initially engaged by the shutter release mechanism during the exposure process.
A common variant in such exposure control systems is to make the shutter from a pair of blades of overlapping configuration and shaped so that as they are moved apart from a closed position a progressively increasing aperture is formed therebetween, this relative motion between the two blades being subsequently reversed to terminate the exposure cycle. Such variable-aperture shutters are typically positioned at a point in the optical train to act as aperture stops, rather than field stops, for obvious reasons.
To provide for proper focusing, many of the more advanced automatic focusing systems provide for a substantial number of pre-established intermediate positions, to any one of which the lens may be driven. A scanning drive is most typically supplied by an energizing spring member, and is most typically terminated by a locking engagement of a pawl or similar mechanism which is electrically actuated to arrestingly terminate the scanning movement of the lens at one of these preset positions. Because of related timing and inertial effects, it is found to be necessary to couple some form of mechanical velocity regulator to the focus drive system to prevent excessive velocity build-up under the action of a drive spring sufficiently strong to give rapid initial acceleration. Here the objective is to secure a rapid acceleration of the system to a moving condition, but to hold the maximum resulting velocity to a reasonable limit so as to allow sufficient time for precise engagement of the stopping pawl, or other mechanism, into proper locking engagement with the focus drive system.
With respect to exposure control, and considering in particular the use of a variable aperture impulse-driven shutter to secure this feature, frequently a variable position shutter blade rebound stop member is employed to control the length of the shutter stroke, and hence the exposure. This stop is similarly spring driven from an initial position through a range of positions. This stop member is similarly locked by an engaging pawl or member at an appropriate position responsively to a control signal from the exposure control circuitry. Such a rebound stop must be similarly rapidly accelerated and thereafter held at a reasonable velocity to allow the locking mechanism to function with adequate precision.
Thus, both drive systems are typically initially cocked to a latched spring-loaded condition, released therefrom attendant to shutter button depression to have their velocities thereafter held at a relatively low value, and then are positively arrested at appropriate terminal positions. After both drive systems have been arrested, the shutter release system must automatically energize the shutter blades, this system also having been initially held in a cocked condition against the force of a shutter spring.
Prior art systems which provide for the necessary velocity-limiting of even a single scanning system, e.g., focus drive, and which provide for properly synchronized actuation of the shutter after termination of the scanning operation, generally suffer from undue complexity or expense, or tend to be wasteful of space. One basic problem which all such systems must cope with is the problem that the scanning system must be capable of stopping at an arbitrary point, after which time the shutter must be synchronously operated. One approach is simply to add an additional velocity limiter to a shutter-actuating member, most typically a spring-energized slide, the slide velocity regulator being arranged to prevent any substantial motion of the slide during the time necessary for movement of the scanning system to its most extreme position, after which time the slide velocity limiter disengages. The slide then is accelerated under the force of its energizing spring to impulsively actuate the shutter blades through an exposure cycle. Such systems require a pair of release latches which, when simultaneously released, release the shutter slide and the drive system from a cocked condition to carry out their respective motions. Furthermore, there must be provided cocking means for restoring both systems into engagement with their respective latches. Such systems are, in general, as stated above, complex.
An alternative approach is to omit the above-mentioned shutter slide velocity limiter, and to use instead a properly synchronized electromagnetic release of cocking the shutter slide from its associated latch. Associated control circuitry is used to operate the shutter latch to a released condition after the scanning drive-terminating control signal has been sensed. Such systems tend to be expensive, as compared to the double velocity-limiter system described above, since they replace the shutter slide velocity limiter at the cost of adding an electromagnet. As in the previous system, provision must be made for returning the scanning drive system and the shutter slide to a cocked condition by engaging a pair of release latches.
It would therefore be a desirable feature to provide in a camera having automatic focus and/or exposure setting capability a greatly simplified mechanical shutter release system.